The invention described herein may be manufactured, used and/or licensed by or for the Government of the United States of America.
The present invention relates to the field of optically controlled phased array antennas/radar and optical signal processing/communication. More particularly, the present invention relates to a simple method and apparatus of creating continuous true time delays in a photonic beam array system which can be used to produce a microwave beam array with the same time delays in order to control/steer the propagation direction of the phased array antenna. It can also be related to a method to make optical analog-to-digital encoding, optical beam steering etc. for the application of optical signal processing communication.
Phased array antenna systems are well known in the art. Such systems can be used, for example. to track objects of interest such as aircraft or missiles. and in high data rate mobile wireless communications. To steer a microwave beam from a phased array antenna one needs to create a time delay xcex94t between the electromagnetic waves generated from each of the neighboring antenna elements in a particular direction. Therefore a time delay array is needed. Traditionally, a time delay was made by a microwave electronic delay device or an electronic phase shifter (not a true time delay). However, for the large number of array elements needed, those electronic devices and waveguides (cables) are very bulky. or very expensive for high frequency systems and yield poor results.
In the last ten years, extensive efforts worldwide have been made to develop an optically controlled phased array antenna in which the time delay arrays are generated in the optical domain and then carry over to the microwave domain using optical fibers. In such a system, size, weight, power consumption are dramatically reduced. There are hundreds of proposed schemes to generate such true time delay arrays, but most of them have significant technical difficulties or have very expensive materials/assembly cost due to their system complexity. In general, for an N-elements antenna most schemes need one laser light source with a lxc3x97N light splitter or N laser sources, and at least 27 (128) switches for each light channel to direct the light to the appropriate true-time-delay (TTD) path. or uses a wavelength division multiplex (WDM) device to distribute multi-color lasers to one time delay generator, then, redistributes by another WDM device the light beams to the appropriate channels for the detectors/antenna elements. Accordingly, there exists a need in the art to have a simplified system to generate the true time delay inexpensively. The present invention can significantly simplify such system by eliminating all the switches, lxc3x97N splitters. WDM devices and is capable of using only a single laser source.
In accordance with the present invention, the above advantages are achieved by providing an optical beam direction the optical beam along a series of N paths of equal length L having U-turns therebetween, providing an identical length change xcex94L for each of the N paths. or an index change in the N optical paths with fix length L, extracting optical sub-beams from the optical beams at the ends of selected ones of the N paths and converting the optical sub-beams to electrical signals.